Process of applying graphite to engine pistons and cylinders



Patented Jan. 29, 1924. p p

UNITED STATES PATENT oFFicE.

JOHN THOMSON, or BROOKLYN, mtw YORK.

' cially fitted thereto.

' PROCESS OF APPLYING GRAPHITE 'I'O ENGINE PISTONS AND CYLINDERS.

No Drawing;

To all whoiim't may concern-.-

Be it known that I, JoHN THOMSON, a citizen of the United States, and aresident of the borough of Brooklyn, city and State' natingsurfaces ofengine-cylinders and their pistons with the objects of diminishingfriction and largely, or even wholly,

preventing them from scoring and seizing.

When first assembled and put into operation, an engine must be coddledand carefully worked-in, otherwise the pistons are liable to jam, byheat expansion, against the cylinder-walls, which frequently results inscoring either or both of the co-ordlnating surfaces, causing them toadhere or, as it is usually termed, freeze. Furthermore, an engine mayrun well up to and at a moderate rate of speed; but, when furtherspeeded-up and necessarily more highly heated, the pistons will befurther diametrically expanded and may impose such an intimacy of.physical contact that admission of oil is prevented, and again damage isliable to ensue. In these circumstances, cylinders must be rebored andnew pistons be spe- The foregoing objec tions are wholly overcome byproceeding according to the present process; which may be thusepitomized:

A process or mode of applying coatings of comminuted graphite uponmetallic surfaces, such as the peripheral surfaces of pistons and uponthe contiguous inner surfaces of cylinders, which shall be so adequatelyadherent to the metal as to subtend the utmost lubrication and endurancepossible to derive from two graphited surfaces, each rubbing upon theother of them.

The preferred material and maneuver whereby to' realize the benignadvantages inherent in this process, will now be set forth.

Thus, the graphite,'preferabl v' artificial,

must be in the form of a dust of molecular-- like fineness and, byaddition of water, be brought to a semi-pasty or paint-likeconsistency,'such asmay be termed an aqua application filed March 17,192:. Serial Io. 826,881.

graphitic do e. An excellent example of ready-to-han material, which ispeculiarly well adapted for this purpose, is the socalled de-floculatedgraphite produced by the process of Acheson, marketed under thetrade-name of Aquadag.

All surfaces, prior to being coated, must be very thoroughly cleansed,as by means of alcohoL The aqua-graphitic' dope is then readilyapplicable by means of a 'soft'brush, such as camels hair. The moistcoating must be left undisturbed until the water therein has completelyevaporated, which is sufficiently evidenced when the dark'pasty dopechanges to a dull grayish-black. Then this dried-out film or platingshould be briskly buffed with cloth, such as wool. canton-flannel orlinen, when the dull graphite takes on a bright, glossy appearance. Theparticular and highly important feature of .this bufiing operation is toset and solidify the graphitic film; and it may be still furthercondensed and more intimately driven into the minute underlying metallicpores by burnishing or planishing. as with polished hardened steel.

If the primary coating is not sufliciently thick, an additionalapplication, or several of them, may be added; but each film should beallowed todry-out before adding another, The thickness of the platingwhich can thus be quite uniformly applied may run from, say, oneten-thousandth up to several thousandths of an inch.

If oil is applied to the glossed surface, graphite is not therebyreleased and floated off; but, on the contrary, may be againcloth-rubbed, effecting what may be termed an oil finish,- the colorthereof becoming somewhat darker than before. Yet, were dry dust mixedwith oil,-this oil-dope being applied to metallic surfaces, the graphitewill not adhere as in the former instance; on the contrary, if rubbedwith a cloth, it will come off with the oil, exactly as .is in the caseof aqua-dope if it is rubbed before the contained water is evaporated. I

It would seem to be a logical assumption that, when the content ofdistilled water is evaporated at atmospheric temperature (and itmay evenbe heated to the vaporiza- .tion point) the graphite would again befound in its primary form of dust; but, the

reasons to the contrary being what they can thus be applied to papertin-foil. lacquer, bu-fi'ed brass. hand scraped surface plates andhighly polished hardened steel. such as needles. Hence, when theapplication is made upon relatively rougher machined or ground surfaceswhich. as micro scopically viewed, present a vast aggregation of hillsand valleys the latter function as graphitic reservoirs and furnish afresh supply as and when the obtruding. hills are elided. Theseimprisoning valleys maybe augmented in depth and area, as by etching,knurling or wire-brushm in gas engines, the pistons necessarily attainand maintain a higher temperature than that of their containingcylinders. Consequently, the practice has become well established to fitpistons. when cold, some thousandths of an inch lesser in diameter thanthe cylinders; the exact amount depending upon the co-efiicient ofexpansion of the metal employed. When started, cold, the annular spacesbetween the pistons and their cylinders are usually sufiicient topermit-an objectionable leakage; and it isduring the period when pistonsare taking heat and expanding that split packing rings play their mostimportant part.

Hence, if pistons can be primarily so closely fitted as to quicklyexpand into actual physical contact, beyond which they becomeself-clearing, then the dutyimposed upon split-rings become merelynominal. Andthat is precisely the condition which is realized by thepractice of this process; for starting with pistons whose. diameters areabout the same as in established practice: with graphitic films addedthereto of thicknesses which will approximately fill the clear annularspaces, when cold, they will self-clear, when expanded, to the nearestpossible amount short of actual physical interlocking of one surfacewith the other of them. In the case of metal-to-metal, scoring andfreezing would undoubtedly ensue; but with graphite-to-graphite theco-ordinating surfaces will planish, condense and rub off until a minuteclearance is eifected, and without possibility of detrimentalconsequences. If oil is present, all well and good; if not, nearlyequally so; for the frictional co-efiicient of graphiteon-graphite is aclose sec-. 0nd to that of oil itself. r

The practice of this method'can also be well extended to the sides ofsplit packing rings and the groove-walls in which they are mounted,whereby their endurance is greatly increased over that of metal-tometalimpingements.

After ashort period of operation, the appearance of. the cylinders andtheir'pistons simulates that of a mirror; consequently, amerely nominalsupply of oil is more efficient than would be a copious supply if therubbing surfaces were metal-to-metal. Per contra, if no oil reaches thegraphitic ,surfaces, the engine runs on; whereas, if metallic surfacesare deprived of oil, the engine stalls. In certain cases, the dope needsbe applied only to the pistons or to the cylinders, as may be preferred,as portions of the applied coatings will be transferred from one to theother of them, the reciprocating movement of the pistons acting toplanish and solidify the co-relating -surfaces.

Erosion of the graphitic films proceeds with surpassing slowness,thereby subtending long periods of satisfactory performance; and eventhen their efiiciency can be quickly restored, at a negligible expense,by the re-exercise of this process.

If a piston is compositely formed of a metal cylinder and solidifiedraphitic rings therein, as in the case of th Patent No. 1,426,022,August 15th, 1922, the aqua-graphitic dope can well be applied to thebearing surface, or surfaces, of the said rings; whereby, if worn down,their desired diameters can be restored.

is applicants While this process has been described in connection withengine pistons and cylinders, it is deemed self-evident that it would bemerely a case of double-use to otherwise utilize it; as, for example, onsliding surfaces and cams of machinery, and on journals, spindles,shafts and their bearings.

What I claim is:

The process of applying adherent coatings JOHN THOMSON.

